A new legal challenge to Northern Ireland's biggest roads project will be heard in June, it has been confirmed.

A High Court judge has set aside four days for a campaign group's bid to halt the A5 Western Transport Corridor scheme.

It means work on the multi-million pound dual carriageway upgrade linking Counties Derry and Tyrone is likely to be delayed until at least the autumn.

In November last year the Department for Infrastructure announced its decision to proceed with the planned route.

The initiative involves a new 85km trunk road running from New Buildings, via Strabane, Newtownstewart, Omagh and Ballygawley, and terminating near the border at Aughnacloy.

Construction on phase one was due to begin in early 2018 at a cost of £150m.

But that was put on hold after fresh judicial review proceedings were launched by umbrella group the Alternative A5 Alliance.

In 2013 the group, made up of landowners, farmers and supporters, won its first legal action against the project.

At that stage a judge quashed the decision to press ahead with the scheme, which forms part of a proposed key cross-border business route linking Dublin and the north west, due to a breach of a habitats directive.

Lawyers representing the Alliance have now brought a new case against the notice to proceed.

One of the grounds of challenge relates to that decision being taken by the Department's Permament Secretary in the absence of a Minister.

Issues around environmental assessments are also expected to feature.

At a preliminary hearing today counsel for the Department said: "The evidence in this case will be very heavy."

The judge, Mrs Justice Keegan, agreed to list the challenge for full arguments over four days in June.

She will also hold a further review in March to confirm details of protected costs arrangements aimed at capping the legal bill in the event of an ultimately unsuccessful challenge.